| Abstract: | Experiments are described in which the responses of wheat stomatato carbon dioxide concentration (0·00, 0·01, 0·02,0·03 per cent.), light intensity (275, 625, 975 f.c.),and rate of air flow (2, 5, 12·5 l./hr.) were studied. Reduction of carbon dioxide concentration from 0·03 to0·01 per cent. resulted in marked stomatal opening; furtherreduction to 0·00 per cent, was accompanied by a slightbut not significant closure. These effects were found at alllight intensities and rates of flow, except at 975 f.c. with2 l./hr. air flow, where no effect of carbon dioxide concentrationwas detected. This last is attributed to excessive depletionof the carbon dioxide supply by assimilation. The apparent lowerlimit of 0·01 per cent, carbon dioxide causing maximalstomatal opening is discussed in relation to recent assimilationexperiments. Increase of light intensity caused considerable stomatal opening,this effect being as great with air of 0·00 and 0·01per cent. as with higher concentrations of carbon dioxide. Thissuggests an effect of light on stomatal movement other thanthat exerted indirectly through photosynthesis by the mesophylcells. Increased rate of flow of dry air caused closure of the stomata;this was shown to be a drying effect and was absent when moistair was used. |
